Control circuit for a hydraulic press



March 12, 1957 w. BRUER ETAL 2,784,619

CONTROL CIRCUIT FOR A HYDRAULIC PRESS Filed OCT'. 17, 1952 2 Sheets-Sheet l a I N. .LCLLLQE l eojrl/ f jy March '12, 1957 w. BRUER ETAL 2,784,619

CONTROL CIRCUIT RoR ARYDRAULIC PRESS United States Patent CONTROL CIRCUIT FOR A HYDRAULIC PRESS Willi Bruer, Coburg, and Otto Oeckl, Kassel, Germany,

assignors to Langenstein und Schemann A.G., Ernsthutte-Coburg, Germany Application October 17, 1952, Serial No. 315,280

Claims priority, application Germany October 27, 1951 17 Claims. (Cl. 78--42) This invention relates to hydraulic presses, more especially drawing presses, with a return cylinder in which a piston is provided for returning the press die.

One object of the invention is to obtain a fast forward and return movement of the press die with the simplest possible means. For this purpose the invention starts from hydraulic presses of the said kind which are provided with a preliminary lling valve which is arranged in the press cylinder, and which is actuated by a hydraulically energised control piston displaceable in a control cylinder, the control piston being movable in one direction by hydraulic pressure and in the other direction by means of a spring force.

Now it has been discovered that this kind of press cylinder. At each entry of pressure fluid into the return cylinder the large preliminary lling valve then opens simultaneously, so that the pressure fluid can ilow back into the replenishing container with hardly any throttling losses. This action is improved still further by amply dimensioning the flow cross section of the preliminary` filling valve. Especially large ow cross sections may be Y obtained by using, as the preliminary lilling valve, a disc valve, the diameter of which is approximately one half,

or preferably three-quarters of the diameter of the work- 2,784,619 Patented Mar'. 12, 1957 ice tainer above the inlet apertures to the preliminary iilling valve to guide the inflowing fluid.

A further object of the invention is to provide the hydraulic press with a device for striking blows, which ing cylinder, and which is arranged in the cylinder head l in the manner known per se.

IIn order-that the control piston may be actuated directly by the working pressure, the effective area ofthe control piston should be small. This is made possible in a simple manner in that the valve stem of the preliminary lling valve is introduced into the cont-rol cylinder, and its cross sections acts exclusively as a pressureenergised control piston. At the same time the valve stem can be guided in the control cylinder by means of a cross-head. In order to prevent movements of the preliminaryl illing valve which are too jerky, it may be provided with a damping means.

LWhen the working piston is shaped as a ditferential piston for effecting the return, and is nevertheless to be returned by the full working pressure of the hydraulic press, the cylinder is provided with an encircling annular space or recess for enlarging the inlet and outlet cross sections in the region of the inlet and outlet apertures of the annular chamber. The working piston may hereby be so dimensioned that only an annular space of very small cross section is formed, the internal diameter of which is for example 24/25 of its external diameter.

With a very fast pressing operation of the working piston, during which the liquid is flowing from the storage container through the preliminary lling valve into the working cylinder, there is the danger of air being sucked in with it. In order to avoid this a wide hood drawn deeply downward is arranged in the storage conpermits rapid and comparatively heavy blows to be struck, which is especially important when using the press for forging work. Moreover the press according to the invention is to -be simple, and is to work as economically as possible.

lFor this purpose the invention consists further in the fact that the working cylinder is connected by means of the suction valve of large ow cross section with the pressure-medium container, and the return cylinder is also connected, by means of a manually controllable return shut-off member of large cross section, with the pressure-medium container. It is hereby made possible for the working piston, together with the platen to plunge down suddenly, the Weight of the platen being increased by the weight of the working piston.

The production of impacts with a hydraulic press according to the invention is facilitated by the fact that according to a further development of the invention the control piston (valve stem) that opens the supplementary suction valve against the .action of a spring is contnuously energised by the pressure prevailing in the return cylinder space by means of a direct connection between.

hydraulic press according to the invention, and consists' in the fact that the supplementary suction valve and the control valve for the entry of the pressure uid into the return cylinder are kept -continuously open during the impact performing stroke, whereas the return shut-off member of the return cylinder is opened for executing each stroke and is automatically closed after the impact.

It is a further object of the invention to provide a structural arrangement of parts operative to constitute what is known as a drop hammer of the type in which van impact member orl platen is carried by a piston slidably mounted in a vertically disposed cylinder and in which means are provided for continuously conveying fluid under pressure to the lower end of the cylinder to `retract. the piston, and which `arrangement vfurther includes discharge means for discharging lluid from the lower end of the cylinder which includes a discharge conduit having an open end, a valve body movable in said conduit in alignment with `the open end and in spaced relation thereto, means for initially moving the valve to a position in which iluid can be discharged from the cylinder responsive to falling movement of the piston whereby upon interruption of the -discharge stream there is created a momentary suction condition operative to move the valve to a position to block discharge so that the continued conveyance of iluid to the cylinder immediately retracts the piston regardless of the length of fall thereof.

Another object of the invention is to provide a hy-r draulic press which can hammer, i. e. which can Work, automatically in the manner of a drop hammer with a rapid sequence of blows, the height and strength of which can be exactly determined.

A machine tool is hereby produced which can execute not only drawing and pressing and single strokes, but

'can also hammer.

For this purpose the invention further consists in the fact that the return-How shut-olf member is automatically controllable for obtaining an uninterrupted sequence of hammer strokes. In order to adjust the height of fall, and thereby the energy of the stroke, as well as the frequency of the stroke sequence, according to a further development of the invention an abutment or tappet, moving up and down with the platen,actuates at acertain height the release member of an electricalswitching device, for example, which opens a shut-off member arranged in the outlet pipe. lf the absolute height of the release member of the switching device or the'height of the tappet in relation to the platen is made adjustable, it is possibleV to determine thel height' of thestroke at will. The invention also relates to the construction `of this switehingdevice.

Anlespecially advantageous method `of operationV can be obtained with the press according to the invention if the controlmembers for the hammeringoperation and thel control members for thev pressing operation are arranged directly adjacent to one another, so that the workman can press and hammer'alternately at short intervals of time;

An especially simple form of constructionV of the hydraulic press is that in whichY a single pistonbelow which liquid is admitted for lifting the ram in the hammering operation and above which liquid is admitted for use as a presspiston islemployed. When using. the sameoperating pressures for hammering and for pressing, this piston kis preferably constructed as al diiferential piston.

Therange of applicability ofthe press according tothe invention can be further extended by providing devices known per se for drawing, such as drawing pads, drawing rings and folded holders. ln this manner a hydraulically operated universal tool is produced which can execute in turn, and in rapid sequence, pressing and drawing, as well as single blows and rapid hammering.

Twov examples of construction of the invention are illustrated in the accompanying drawings, in which:

Figure l shows a hydraulic press according to the invention which can execute single strokes; and

Figure 2 shows a hydraulic press according to the invention which can in addition strike in rapid sequence, i. e., in the manner of a drop hammer;

Figures 3 and 4 show individual parts of the control device of Figure 2, Figure 3 being a plan view looking in the direction III- lll of Figure 2, and Figure 4 being a side View of the individual part on the line lV-IV of Figure 3.

Figure l is explained as follows:

The working piston or ram 2, constructed as a difterentialpiston, is capable of moving in a working cylinder 1. The stepy 2a shuts oif the pressure chamber 3, whilst the step 2b forms with the cylinder 1 an annular chamber 4'operating as a return cylinder, the internal diameter of which is approximately 1/5 smaller than its external diameter. The lower part of the cylinder is of increased internal diameter so as to provide an annular enlarged space or recess 4a in the region of `the inlet and outlet apertures at the lower end of the cylinder. In the cylinder head 8,7851, with passage channels 5a, is arranged a disclike surge valve 6, hereinafter called a supplementary suction valve, which closes an opening in the cylinder head, the diameter of which valve is approximately threequarters of the cylinder diameter, and the valve stem 7 of which passes through a valve-guiding body 8, the lower part 8a of which shuts on the cylinder 1, the valve stern 4then projecting into a control cylinder 9. There the valve stem 7 is guided through a cross-headl 10, which has holes, not illustrated here, for the pressure liquid, and is subject to the action of a pressure spring 11, which is so dimensioned that it can close the valve 6 with a small pressure. Into the control cylinder 9 a pressure pipe 12 opens, which can deliver pressure uid from a preferably continuously running adjustable delivery pump 13. The pipe 12 is in constant communication with a pipe 14,

which opens into the annular chamber 4a and feeds fluid to chamber 4 between the working cylinder 1 and the stepped piston 2b. By means of a pressure pipe 15 liquid under pressure can be introduced into the Working chamber 3 at 15a for producing the pressing stroke. The controlling of the fluid into the pipe 15 or into the intercommunicating pipes 12 and 14V iseffected in a manner known per se by means of a control lever 16, which is rotatable about an axle 17 and actuatesa control rod 18', which, by way of a bell-crank lever 19 and a link 20 actuates a two-armed lever 21, which, in a known manner, can allow pressure fluid to flow alternately into the pipe 15 `or into the pipes 12 and 14, and in its mid position illustrated doesV not allow any pressure fluid to escape. On that side of the working cylinder 1, which is opposite to the entrance of the pressure pipe 14, there is connected to the annular chamber 4a a further pipe 39, which, in the tank 38, `open at 38b, has a shut-off member 22. This shut-off member is shown in the drawing in the closed position, and can be opened by means of a hand lever 23, pivotable about a fixed axis 24, by way of a control rod 25 and a two-armed lever 26. The two-armed lever 26 engages by means 0f a link 27 with a slide-valve piston 28, the sealing edge 29 of which in the position illustrated, lies somewhat below the lateral inflow openings 30, through which liquid under pressure from the pipe 39 can enter the rather long axially arranged lower outlet pipe 31 as soon as the slide piston 28 is drawn up. To the inlet Aopenings 5a arranged on all sides a cap or hood 6b is connected, which extends downwards deep into the liquid in the replenishing tank 3S. It prevents the suction of air. By means of the described construction and arrangement of the shut-off member 22, and on the cessation of the fluid return as a result of the inertia of the huid flowing out in the outlet pipe 31, a strong pull acting in the closing `direction is exerted upon the slide piston 28, so that a rapid closure of the slide piston is effected. Since the direction of outllow is downwards, the weight of the pressure liquid therein also acts in the closing direction. Sincerthe outliow pipe 31 of the return slide valve opens intothe storage tank 38 for the suction valve 6, 6b, the outlet pipe 31 is preferably allowed to open below the lowest surface level of the liquid, so that no air is swirled into the liquid in the storage tank by means of the'returning pressure medium. The levers 23 and 16 are, in practical construction, placed so near to one another that they can be operated by one workman.

If, with the press according to this example of construction, working pressure is to be exerted, the lever 23 remains in the position illustrated. If the hand control lever 16 is depressed in the direction of the arrow 33, pressure liquid is then delivered in a known manner throughthepressure pipe 15 to the working piston or ram 2, so that the latter is displaced downwards, with the ram. The suction valve 6 hereby closes automatically. If. the hand lever 16 is thereupon brought back into ythe mid position illustrated, the press remains staf tionary. On lifting the hand lever 16, pressure fluid passes throughthe pipe 12 into the control cylinder 9, andth'rough the pipe 14 into the annular space 4, so that the working piston or ram 2 is quickly raised, the pressure liquid in the cylinder space 3 then being able to ow back through the suction valve 6.

The, tube 14 is in communication with reservoir 38 by a tube portion 14' having a one way valve 60 at the end thereof. The valve 60 permits liquid to ow from reservoir 38 to pump 13, when the latter is sucking, so that the pump can deliver liquid into cylinder 3. The valve 60 normally prevents reverse ow of liquid from the pump to the reservoir 38. If pressing is to be eifected, they pumpV sucks liquid simultaneously from annular chamber 4 and reservoir'33. Valve 66 can be provided with known mechanism, notv shown, which would permit-opening of thislvalve by hand when the pump is not sucking. When such is done, the liquid which is' in pressure chamber 9, annular chamber 4, and conduits of the hood 6b here prevents the entry of air into the working cylinder, which would otherwise inevitably disturb the operation. v

The crosshead-like guiding part 10 may be constructed as a perforated disc, and then serves for damping the hard movements of the valve 6, since the pressure liuid, during the reciprocating movement of the valve 6, has to pass 4through these holes in the guiding part, a throttling resistance thus being provided. Instead of providing holes in the guiding part 10, recesses may be pro-y vided on its edge, so that slots are formed between the guiding part 10 and the wall surface of the control cylinder, through which uid must pass. The arrangement for damping may of course also be adopted when the guiding of the valve stem by means of a crosshead is omitted.V

When hammer strokes are to be eiectedwith the press, the hand lever 16 is first lifted so that the working piston 2 ascends with a platen 34 until either -the piston bears against the suction valve 6 or the platenv34, withran arm 35, raises a tappet 36 which is mounted on the control rod 18, and thereby returns the hand lever` 16 into the mid position illustrated, so that further admission of pressure fluid into the annularspace 4 is interrupted. When a blow is to be struck the hand lever 23 is pulled down and the slide piston 28 thus raised.

Consequently, under 'the weight of the working piston 2 and the platen 34, the pressure fluid flows from the cylinder space 4 by pipe 39 through lthe shut-off member 22`into the storage tank 38. At the same time the suction valve 6 opens automatically, since when the piston falls, .fluid ows out of pipe 39 causing the lspace on top ofthe piston `to enlarge and to permit the fluid pressure in pipe 12 :to overcome the pressure of spring 7 so that valve 6 opens. As soon as the stroke has been m'ade the valve 22 closes automatically, since the uid flowing through the outlet pipe 31 exert-s as a result of its mass -a suction force which acts -almost exclusively upon the piston 28, since only very small amounts of pressure fluid can flow out of the .annular chamber 4. The length of Ithe pipe 31 is dimen- .sioned according to the required closing force, it `being advantageous to guide the pipe in a downward direction, vso that the weight of the liquid inside the pipe assists the l.closing force. The introduction of the pipe-31 below the liquid surface level 38a is desirable so that pressure means flowing from the pipe 31 does not swirl any air into the liquid. During the hammering operation the hand lever 16 may remain in the raised position, so that during ,the whole striking operation pressure fluid is being uninterruptedly introduced into the annular space 4. The loss of output caused by this is small, since during the fall of the piston 2, in spite of the opening of the non-return member 22, another' small pressure exists in the annular :spa-ce 4, which arises lowing to the friction losses of the oil stream in the pipe 39, the sli-de valve piston 28 and the connecting pipe 31. Directly after the impact, after which the piston therefore exerts no more pressure on the Huid, the shut-off piston y28 is however closed `and the continued entry of uid into space 4a from pipe 14 immediately initiates retraction of 'the ram or piston.

The references 1 to 22, 28 to 31, 33, 34, 38 and 39 in'Figure 2 indicate the same parts as the referencesin Figure 1. The press according to Figure 2 differs yfrom the press illustrated in Figure l in that with it repetitive hammer strokes following quickly on one another can 'be effected without -a special hand actuation being necessary for each individual stroke.

The control lever 16 in Figure 2 is provided with an `attachment or lug 16a, against which a locking lever 32 with a projection 32a can be placed, in order to prevent with certainty the ow 4of pressure uid into the pressure chamber 3 during certain methods of operation. The control piston 28 of Figure 2 can be raised with lthe help of electro-magnets 58, which by means of contacts 40 can receive current. The contacts 40 4are actuated by means of `a relay 41, which is inserted in a circuit 42u, 42b, which is provided with an interrupter switch 43 and a press-button switch 44. The press-button switch 44 can be actuated by hand, whereas the -switch member 45 of the switch 43 can be actuated by a switch body l46, which is mounted fast with a sleeve 47 on a switch rod 48. The switch rod 48 is rotatably mounted in bearings 49 and 50, and carries by means of a sleeve 51 Aa release lever 52, which projects into the region -of an abutment 53 which is secured to the platen 34 of the drop hammer. The abutment 53, as shown in Figure 4, has a rounded shape, so that during the upward and downward movements of the ram 34 it can turn the `release lever 52 about the Iaxis of the control shaft 48 suitable means not shown restoring shaft 48 to the position in which lever 52 is in the path of movement 4of abutment 39. On rotating the release lever thus takes the control shaft 48 along with it, so that the switch body 46 opens or closes the switch 43. The sleeve 51, which is non-rot-atably mounted on the control shaft 48, can be adjustably displaced axially along the control shaft 48 and then be secured in adjusted position. In order that single strokes may be made with the platen, either a hand lever 54 can be arranged on the switch rod 48 or a hand-actuated switch 57. can be arranged in -a bridging conductor 55, 56 on the conductor 42a leading to the relay 41.

When a repetitive hammering operation is to be carried out with the press, the preliminary filling valve 6 is opened by admitting pressure liquid into the control cylinder 9 by rocking the hand lever 16 upwards opposite the direction of the arrow 33. The valve 6 therefore remains constantly open, and the pressure uid supplied Iby the pump 13 has constant access to the annular space 4. At the same time the press-button switch 44 is closed. lf during the upward movement of Ithe platen 34 the `abutment 53 touches the release lever 52, it turns the control rod 48, so that the switch member 46 closes the contact 43. rlhe relay--circuit 42a, 4211 is thereby closed, so that the relay 41 energizes the magnets 58, which pull the piston valve 28 upwards. Thereby pressure iiuid now p-asses Ifrom the annular space 4 through the pipe 39 under the piston valve 28. Since the inflowing pressure fluid still has a considerable pressure the piston valve 28, even on the de-energization of the magnets 58, cannot close so long as ythe fluid stream continues through the return pipe 39. On the impact of the platen 34 on the work piece the return ow of the pressure uid ends, so that the sealing edge 29 of the piston valve 28 closes the openings 3% as `a result of its own weight. The closing movement is further strengthened in that the pressure fluid in the outlet pipe 31 exerts a suction force on the piston 28. After the closing of the return pipe 39 the piston or ram 2 is raised again immediately, since now `the pressure fluid owing through the pipe 14 correspondingly raises the pressure in the annular space 4. The -disc valve 6 remains open, since the working pressure in the control cylinder 9 continues. A continued hammering operation therefore takes place, which continues until the pressbutton 44 is released. The lock 32, which, during the hammering opera-tion, is preferably engaged, prevents the lever 16 from being erroneously depressed during the hammering operation.

A single stroke can be effected by a brief depression of the' press-button 44r(whilst actuating the hand lever 54 at'the same time), or by actuating the hand-switch 57, Iand this can be done from any required height.

If a pressing operation is to be effected with the press, the release lever 52 is adjusted toand maintained at its uppermosty position where cam 53 will not contact the same, a hammering, however, isnot effected, as the switch 44 is not closed by hand. lf a single stroke is ydesired from a height other than that which is determined by the height of the lever 52, the switch 57 is closed, so that the platen 34 falls down from lthe height, which it possesses at that moment, when the switch 57 is closed.

yIt is believed clear, therefore, that the present invention provides `an improved control arrangement for Ia piston carried impact member, the piston of which is slidable in a cylinder. The control arrangement being such as to include means for conveying fluid to the lower portion of the cylinder to retract the piston, means for discharging fluid from the lower portionV of the cylinder operative to discharge fluid responsive to falling of the piston carried impact member even though fluid is still `being admitted to the lower end of the cylinder. The discharge means including a conduit having an open end, `a valve body slidable in the conduit in spaced relation to the open end, lateral ports controlled by the valve body and means for at least initially moving the valve body to expose the ports whereby a continuous dis-charge of fluid through the ports and past the valve body exists as long as the piston is falling. However, upon impact, the continuous stream of fluid `being discharged is interrupted creating at least a momentary suction condition operative to move the valve body toa position to close the ports so that the continued introduction of fluid immediately initiates retractionof `the piston. There is thus provided an arrangement in which a retraction is effected immediately upon impact eliminating rebound and the automatic control of retraction permits impacting work of any vertical dimension without making any adjustments whatsoever.

As a further development, the invention provides a control whereby the piston carried member can make repetitive impacts and in which the height of fall can be adjustably determined. In accomplishing this result, the invention includes hammer actuated control members operative to initiate movement of the discharge control valve to open position in response to av selected upward movement of the hammer.

lf only a hydraulically actuated drop hammer is to be produced which is not capable of pressing and drawing, the devices serving for the pressing operation are omitted, so that in particular air or liquid can at any time enter and escape by way of the piston or ram 2.

We claim:

l. A control circuit for a hydraulic press having a ram reciprocable in a cylinder and a platen carried by the ram, such circuit comprising fluid operable advancing and retracting means operatively associated with the ram and cylinder, a fluid reservoir, a surge valve means between `the advancing means and the reservoir, fluid operable meansincluding a direct uninterrupted connection with the retracting means and responsive to a predetermined pressure therein to open the surge valve means, a reversible delivery fluid source connected to the advancing and retracting means, selectively operable means associated with the fluid source to `control the direction of delivery of the fluid source to reciprocate the ram and platen, a shut-ofr` device operatively connected with the retracting means to exhaust the sarne independently of the connection between the fluid source and the advancing and retracting means to obtain a gravitational advance of the platen and means connected with the shutoff device automatically closing said device by the platen striking a work piece.

2. In a fluid press according to claim l, in which said shut-ofi device comprises a balanced control member ha"- ing av displaceable slideA piston, a controlV cylinder in'which; the*J piston` ist slidable at least one lateral inlet aperturey arranged'in the control cylinder adapted to be closed by the piston, outflow from thecontrol.cylinderfbeingeffected through a-front sideV opening of the cylinder, and anoutlety pipe atl-the lower end of the control cylinder in communication withthe front side opening.

3. In -a fluid-press according toclaim 2, in which the outletpipeV extends into the reservoir, saidreservoir being arranged. on the pressfor the preliminary fillingv of a chamber of the ram cylinder, the lower endy ofy the outlet pipe being disposedI below the lowestl liquidvsur-face level insaid-reservoir.

4. Ina press according 'to claim l, in which said surge valve is providedv with entry apertures surrounded by a hood, said hood extending downwardvr to a considerable depth in theV reservoir and adapted to guide inowing fluid to said apertures.

5. In a press according to claim l, having control means associated withthe said shut-off device to obtain an uninterrupted sequenceof hammer strokes, Vsaid control meansbeing operative to open the shut-off device automatically, as soon as the platen has been raised -to a predetermined height.

6. InA a' press according to claim'l, in which the means connected to the shut-off device includes an electrical operating means, a release member therefor, an abutment mounted-on saidplaten which at ay certain height of the pl-atenactuatessaid release member for opening the said shut-oilV device;

7. In a press according to claim 6, in which the release member is adjustably mounted on a switch control rod of: the electrical operating means, and :thelieight of theV abutment is adjustable" in relation tov itheplaten.

8a In a press according to claim l, in which the means connected to the shut-off device includes an electrical operating means,` al release member mounted on a switch control shaft, a curved abutment arranged on said platen, which as the latter 'is movable up and down, turns by means of the release member said control shaft which in turn actuates a switch of a relay adapted Ito energise an electro-magnet for openingthe said shut-off device.

9. In a press according to claim 8, having a second switch actuated by hand, and which is arranged in the circuit of said relay.

l0. In apress according to claim l, in which the means connected to the shut-off device includes an electrical operating means, a release member mounted on a switch control rod, an abutment mounted on said platen which at a certain height actuates said release member for automatically opening of said cut-off device, `and a hand lever on said control rod. for effecting single strokes, said hand lever being independent of the automatic opening arrangement opening the said cut-off device.

1l. In a press according to claim l0, in which a hand operated switch for effecting single strokes is disposed in a bridging element of a conductor leading to a relay adapted to energize an electro-magnet for opening the said cut-off device.

l2. In a fluid controlled apparatus of the type in which a work performing member is carried by la piston slidably mounted in a cylinder, a control arrangement comprising means for admitting fluid under pressure to one end of the cylinder to retract lthe piston, a fluid reservoir, conduit means extending from said end of the cylinder to the reservoir, and control means governing the retracting movement of the piston comprising valve means operably associated with said last mentioned conduit means, said valve being mounted for movement between a first position interrupting the flow of fluid through said conduit means and a second position in which fluid can flow through the conduit means lto discharge fluid from said end of the cylinder permitting advancing movement of the piston, means for initially moving said valve to said second position,V said valve including a face impinged upon by the fluid during discharge when the valve is in 'said second position whereby said valve is maintained in said position as long as said position is advancing and responsive to cessation of advancing movement of the piston the fluid being discharged has insuiiicienlt force to maintain said valve in said second position whereby it automatically closes.

13. A control circuit for a drop hammer mechanism of the type in which an impact member is carried by a piston movable vertically in a cylinder, said control circuit including means for continuously conveying fluid under pressure to the lower end of the cylinder to retract the piston and elevate the impactmember, a reservoir, discharge means for discharging uid from theV lower end of the cylinder at a rate in excess of the rate of admission of the tluid whereby the piston can drop due to the combined weight of the piston and impact member, said discharge means including conduit means having an open terminal end communicating with the reservoir, a discharge control valve operably associated with said conduit, means within the same and including a body portion mounted for movement coaxially of the open end, said conduit means including port means controlled by said body, means for moving said body in the direction away from said open end to expose said port means whereby uid discharges into said reservoir and in flowing through the conduit means and said port means impinges upon said body and creates a continuous fluid stream extending between said body and the terminal end of the conduit means whereby said valve body is maintained open as long as the piston is advancing and upon cessation of advance of the piston occasioned by an im pact of said impact member said continuous stream is interrupted creating a momentary suction condition in said conduit means between said valve body and the open terminal end whereby said valve body is automatically moved to closed position locking iiuidvin said conduit means between said port means and said cylinder whereby the continued ow of uid into said cylinder retracts the piston and the retraction ofthe piston commencing irnmediately following impact regardless of the length of fall of the piston.

14. A control circuit for a drop hammer of the type in which a vertically disposed cylinder guides a piston carried hammer member and comprising controllable means for admitting uid under pressure to the other end of the cylinder to elevate the piston carried drop hammer and means for controlling the drop of said hammer comprising discharge conduit means communicating with the lower end of the cylinder and through which fluid is discharged responsive to dropping of the piston, said .s

discharge conduit means including a vertical portion having an open terminal end, lateral port means incorporated in said vertical portion in spaced relation to the open end, valve body means slidably mounted in said portion in alignment with the open end and adjacent said port means and adapted to cover or uncover the same, means for 10 initiallymoving said valve body means to a position to uncover said port means whereby downward movement of the piston effects discharge of uid through said port means past said valve body and out said terminal end in a continuous stream impinging upon said valve body to maintain the same open, impact of said hammer interrupting said continuous stream and creating a momentary suction condition between said valve body and the openk end to move the body at least to a position to cover said port means whereby the means for admitting tluid to the other end of the cylinder are operable to elevate the piston.

15. A control circuit for a drop hammer of the type in which a piston carried hammer member mounted for vertical movement in a cylinder having a lower end through which fluid is admitted for retracting the piston, said circuit including means for discharging uid from the lower end of the cylinder to permit the hammer to fall including conduit means within which a continuous' ow of fluid exists as long as the hammer is falling, said? conduit means having an open terminal end, valve means slidably associated within said conduit in spaced relation to the said open end, means initially moving said valve* means to a first position in which iluid can ow through said conduit means and said valve means closing auto-fv matically responsive to cessation of continuous iiowl through said conduit means occasioned by impact of said; hammer. f

16. In a control circuit for a drop hammer mechanism? as claimed in claim 13 and hammer actuated means oper able in response to retraction of the piston and operably;` associated with the means for moving said discharge con-v trol valve body in the direction away from the open end of the discharge conduit means to effect discharge of fluid from the lower end of the cylinder inresponse to retraction of the piston whereby the piston again falls to repeat an impact operation.

17. In a control circuit for a drop hammer mechanism v as claimed in claim 16 in which said hammer actuated means include a vertically adjustable movable control element, operably associated with the means for moving said body and operable to effect movement of said body When the control element is moved and an abutment memberl carried by the hammer and engageable with said control element during retraction of the piston.

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